<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 50px;
            height: 50px;
            background: url(images/bgs.png) no-repeat -159px -51px;
            position: fixed;
            right: 10px;
            top: 40%;
        }
        
        .erweima {
            position: absolute;
            top: 0;
            left: -150px;
        }
        
        .box a {
            display: block;
            width: 50px;
            height: 50px;
        }
        
        .hide {
            display: none;
        }
        
        .show {
            display: block;
        }
    </style>
</head>

<body>
    <!--
        题目要求: `<div class="erweima hide" id="er">`，将class的属性值中的hide更换为show，其他保持不变，请写出适合的方法。
      -->
    <div class="box" id="box">
        <div class="erweima hide" id="er">
            <img src="images/erweima.png" alt="" />
        </div>
    </div>

    <script src="common.js"></script>
    <script>
        // 获取元素
        var box = my$('box');
        var er = my$('er');

        // 鼠标移上元素时触发的事件
        box.onmouseover = function() {
            er.className = 'erweima show'
        }

        // 鼠标离开元素时触发的事件
        box.onmouseout = function() {
            er.className = 'erweima hide'
        }
    </script>
</body>

</html>